The present invention relates to protective coating compositions and articles coated therewith. More particularly, the present invention relates to a method for applying a second silicone resin coating composition over a first silicone resin coating composition which has become scratched or marred, or which requires a tint.
Recently the substitution of glass glazing with transparent materials which are more resistant to shattering than glass has become widespread. For example, transparent glazing made from synthetic organic polymers is now utilized in public transportation vehicles such as trains, buses and airplanes. Lenses, such as for eyeglasses, as well as glazing for large buildings also employ such shatter resistant plastics. One of the most promising and widely used transparent plastics is polycarbonate, such as that known as LEXAN.RTM., sold by General Electric Company.
While transparent plastics provide the advantage of being more resistant to shattering than glass, a serious drawback lies in the ease with which these plastics mar and scratch due to everyday contact with abrasives such as dust, cleaning equipment and ordinary weathering. Continuous scratching and marring results in impaired visibility and poor aesthetics, and oftentimes requires replacement of the glazing or lens.
Accordingly, attempts have been made to improve the abrasion resistance of transparent plastics. It has been found that silicone resin coating compositions are among the most effective protectants available. Such silicone resin coating compositions were first disclosed by Iler, U.S. Pat. No. 2,786,042, in 1957. More recently, silicone resin scratch-resistant coatings formed from mixtures of silica, such as colloidal silica or silica gel, and hydrolyzable silanes in a hydrolysis medium, such as alcohol and water, were disclosed in U.S. Pat. Nos. 3,708,225, 3,986,997 and 3,976,497. The latest improvements in silicone resin coating compositions are described in U.S. Pat. Nos. 4,177,313, 4,277,287, 4,299,746 and 4,309,319 and in copending U.S. patent application Ser. No. 964,910, filed Nov. 30, 1978. Each of the aforementioned disclosures is hereby incorporated by reference into the present Application.
Although a transparent plastic coated with any of these hard coating compositions is provided a highly desirable protective finish, eventually such hard coating compositions will become scratched or marred. Heretofore it has not been possible to apply a second or refinishing silicone resin coating composition to the first coating composition because of the inability of such second coating to adhere thereto.
The present invention, however, provides a method whereby the surface of the first hard coating composition is etched with a caustic solution so as to provide a surface to which the second or resurfacing coating will readily adhere. The present invention also provides a means for applying a tint to a transparent plastic substrate by utilizing a dye-containing silicone resin hard coating composition applied to the surface of such transparent plastic substrate.
Accordingly, it is an object of the present invention to provide a method for resurfacing a scratched or marred first silicone resin hard coating compositions with a second silicone resin hard coating composition to restore the marred surface to substantially its original condition.
It is another object of the present invention to provide a means for applying a tint to a transparent plastic substrate by utilizing dye-containing silicone resin hard coating composition cured to the surface of such plastic substrate.
Other objects and advantages of the present invention will become obvious from the following detailed description.